Table-per-hierarchy inheritance

Question

Table-per-hierarchy inheritance

Vojislav Ćeklić 1

Hi there,

I have created inheritence

public class Item
{
int Id;
string SerialNumber;
......

}
public class Phone : Item
{
Model PhoneModel;
string ScreenSize;
......
}
public class Sim : Item
{
string PhoneNumber;
.......
}

What is the best way to get Items with all properties for both Phone and Sim?

If I create entity that will hold all items (something like shopping cart) what is the best way to distinguish what is type od item. Thanks

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Answer 1

Daniel Zhang-MSFT 9,661

Hi Vojislavekli-7484,
>>What is the best way to get Items with all properties for both Phone and Sim?
Query basic entities(Item) will get the results of all entities in the hierarchy.
If I misunderstood what you mean, please explain in detail.
>>what is the best way to distinguish what is type od item.
TPH uses a single table to store the data for all types in the hierarchy, and a discriminator column is used to identify which type each row represents.
The discriminator can be configured to distinguish different types.
More details please refer to this document.
Best Regards,
Daniel Zhang

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Vojislav Ćeklić 1 Reputation point

2021-08-05T12:31:30.5+00:00

Thanks for your answer. You are right, it returns them all, but just properities defined in basic entery (item) not in derived ones. I would like to have list of all items with persepctive properties, for i.e.:

ITEMS

ID Serial Number Screen Size Phone Number ....................... Action
1 1234 5" Null Borrow
2 009ABC Null 416-989-5554 Borrow
3 1233 6" Null Borrow
4 08A555 Null 416-998-555 Borrow

Idea is to have this list, so I can click "Borrow" and put this item in Table that holds history of borrowed items (regardles of type)
I hope this is a bit clearer for you.

For second part I learnt that I could use : var p = Item.GetType() or if(item is Phone)

Thanks a million.
Daniel Zhang-MSFT 9,661 Reputation points

2021-08-06T02:23:20.603+00:00
Hi @Vojislav Ćeklić ,
You can try the Polymorphic Queries which queries all instances of a class and its subclasses respectively.
Code looks like:

public class EntityContext : DbContext { public DbSet<Item> items { get; set; } } var query = context.items.ToString();

More details you can refer to this document.
Best Regards,
Daniel Zhang
Vojislav Ćeklić 1 Reputation point

2021-08-06T06:46:39.787+00:00

Thanks DanielZhang-MSFT,

I do not have context.items.ToString();, there are just .ToList(), ToArray(), ToDictionary(), ToLookup, ToHashSet......no ToString method on this DBSet.

I tought I could do DTO, that I can manually populate, since I just need this for views.
I will try something.
Daniel Zhang-MSFT 9,661 Reputation points

2021-08-06T07:19:41.167+00:00

Hi @Vojislav Ćeklić ,
.ToString() is supported properly going forward with EF 6.1.
Best Regards,
Daniel Zhang
Vojislav Ćeklić 1 Reputation point

2021-08-06T07:22:10.933+00:00

Sorry, I just put a tag that this is a EF Core 5 Anyhow thanks for your help.

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